The present invention relates generally to deep well pumps of the type used to recover subterranean oil deposits, and, more particularly, to deep well pumps of the type in which the pumping motion is originated at the surface of the ground and transmitted through a reciprocating string of rods to a pump located within the well bore. Yet more particularly, the present invention is especially concerned with an improvement in the efficiency with which the fluid and mechanical loads imposed upon the pumping unit of the type described may be counterbalanced.
In deep well pumps, such as oil well pumps, of the type in which the pumping motion of the subsurface pumping equipment originates at the surface of the ground (as opposed to subsurface pumps in which the pumping motion originates below the surface of the ground), effective counterbalancing of the pumping unit to reduce the load on the prime mover and power translating equipment is extremely important. Irregularities or inequalities in loading that fall upon the sucker rods during different parts of the pumping cycle impose a difficult operating problem on the prime mover, tending to cause irregularities in speed and creating a variable and rapidly fluctuating power demand. With regard to fluctuation in power demand, if, for example, the energy source for the pump prime mover is electric, these irregularities imposed on the power demand require that the entire electrical system for the pump including the source and the motor be rated for peak amperage demands. Thus, in improperly counterbalanced pumping systems, not only must more expensive motors and power hookup connections be supplied, but in addition, the cost of the electrical energy supply is increased, as it is metered on the basis of peak current loads or demand.
Furthermore, regarding structural failures, in conventional oil well sucker rod pumps, it has been estimated that about 90 percent of the failures of speed reduction gearing, pitmans, bearings and shafts result from improper counterbalancing. The primary purpose in counterbalancing a pumping unit is to reduce the effective peak load on the prime mover, the energy source for the prime mover, and the gear box through which the prime mover drives the unit so that smaller engines, less fuel or energy, and less massive speed reduction gearing can be employed. This in turn results in great economic savings, since it is less expensive to supply counterbalancing weights than it is to provide the heavier, more complicated engines or motors and gear reduction systems, and more expensive fuel or energy consumption costs necessary to drive the pumping unit without the assistance of effective counterbalancing.
In an ideally counterbalanced system, the total load imposed upon the pumping unit by the fluid load lifted by the pump, plus the weight of the rods and losses due to friction, etc., would be substantially completely offset by a counterbalance applying an opposing force to the motor. However, the systems heretofore most widely used have at best been effective to counterbalance a downwardly acting force equal to the weight of the rods used to pump the liquid, plus one-half of the weight of the fluid lifted by the pump. Under this arrangement, the net load lifted during the upstroke of the pump equals the load applied to the pump through the sucker rod string less the countereffect of the counterbalance. Since, during the upstroke, the static load on the pumping equipment consists essentially of the weight of the rods plus the weight of the fluid, the net load on the system when the counterbalance effect is subtracted equals half of the weight of the fluid lifted. On the downstroke, on the other hand, the net load equals the counterbalance weight less the weight of the falling rods, or again, approximately half the weight of the fluid lifted on the upstroke. The net load on the prime mover and gear box is therefore equal during the upstroke and the downstroke. Thus, the peak load occurring during each stroke is considerably less (by the amount of approximately half the weight of the fluid load) than the peak load imposed on the unit through the sucker rod string without benefit of any counterbalancing. Nevertheless, in such conventional counterbalancing systems, the loads imposed on the prime mover are not fully counterbalanced throughout each pumping cycle, as the load of approximately half the weight of the fluid load during each stroke is not counterbalanced.
For a number of years, efforts have been directed to the more effective counterbalancing of the torque imposed on the prime mover and gear reducer of deep well pumps of the type described. Generally, however, such efforts, while in some instances being effective to reduce the peak torque transmitted to the driving mechanism from the rod string, have increased the cost of the pumping unit to the extent that an improvement in counterbalancing over that which is most widely currently attained has not been found to be economically justified. In addition, such efforts have also resulted in counterbalancing systems wherein the center of gravity of the counterbalancing weight for the pump jack travels in a vertical pattern of movement throughout each pumping cycle which takes on the configuration of a straight line, an oval or a circular configuration. When the center of gravity of the counterbalancing weight simply travels up and down in a straight line throughout each pumping cycle, the counterweight is not being effective to compensate for inequalities in loading that fall upon the sucker rods during different parts of the pumping cycle. The same holds true when the center of gravity of the counterbalancing weight travels in a pattern of a uniform or balanced oval or circle throughout each pumping cycle, as the loading which falls upon the sucker rods during the different parts of the pumping cycles does not vary with such uniformity or regularity during and when transitioning from and to upstrokes and downstrokes of the pump. Also, while some of the pump counterbalancing systems of the prior art do improve the problem of counterbalancing against the irregularities in loading during different parts of the pumping cycle, they do not, to a desirable degree, effectively redistribute the load placed on the prime mover and gear box throughout each pumping cycle to a more uniform load distribution.
One of the earlier efforts to depart from the conventional counterbalancing technique was that of V. A. Nicolescu described in U.S. Pat. No. 2,286,153. In this system, Nicolescu utilized the lemniscate linkage system and parallelograms in order to convert rotary paths of the pump drive and/or walking beam into rectilinear paths in order that the sucker rods and the counterbalance weight will move up and down during pumping cycles in vertical parallel paths of movement. Thus, while the Nicolescu structure insured rectilinear movement of the sucker rods, it did not resolve the problem of counterbalancing to compensate for the irregularities in loading that fall upon the sucker rods during different parts of the pumping cycle.
Another effort to more effectively counterbalance the well load suspended from the walking beam is disclosed in Downing U.S. Pat. No. 2,432,735. In the Downing Patent, a counterweight is slidably mounted on the walking beam and is shifted by a hydraulic cylinder carried by the walking beam in a properly timed sequence to counterbalance the well load. The system, however, still required a separate prime mover and gear reduction system for driving the walking beam in an oscillating movement which would synchronize with the activation of the weight shifting hydraulic cylinder. In addition, the system does not compensate for the fact that as the counterweight in either position shifts on the end of the walking beam and travels up and down with the walking beam, its center of gravity travels in an arc created by the pivotal movement of the walking beam about the Samson post pivot, thereby undesirably changing the effective counterweight during each stroke.
Other efforts at improving counterbalancing effects by mounting a shifting weight on the walking beam of the pump whereby changing the moment of the counterweight are described in Mitchell U.S. Pat. Nos. 2,940,335 and 2,995,048, and Chastain 2,841,992. Chastain's system in particular claims to go far towards reducing the peak load imposed on the prime mover and speed reducer during both the upstroke and the downstroke as a result of changing the effective moment of the counterbalance by changing the leverage of the counterweight as it is applied to a crank arm connected directly to the speed reducer. This, in fact, is a desired advantage. However, two of the systems require the addition of a second prime mover to move the counterweight, and these systems still cannot adequately or economically compensate for the loading irregularities to the degree required by present energy demands, particularly in view of the high cost of manufacture of these systems.
Another counterbalancing system for deep well pumps is illustrated in Scoggins U.S. Pat. No. 3,209,605, wherein the counterbalancing weight is reciprocally mounted on the walking beam, and the prime mover for the pump is also mounted reciprocally on the mounting beam and imparts oscillating motion to the walking beam as well as reciprocating motion to the counterbalance weight. The counterbalancing weight is moved in a generally circular path or pattern of vertical movement during pumping cycles. As previously pointed out, movement of the center of gravity of the counterweight through a vertical path of movement which is balanced or uniform in the form of a circle cannot fully compensate for the inequalities in loading that fall upon the sucker rods during different parts of the pumping cycle, as the variations in loads between upstrokes and downstrokes of the pump and transition between these strokes does not vary in such a uniform manner. It is this basic principle that, while the prior art may show improvements, it does not adequately compensate for when considered in conjunction with other considerations such as cost of manufacture of the pump jack in combination with the ability to change the leverage of the counterweight as it is applied to the crank arm to accordingly reduce the peak load imposed on the prime mover and speed reducer and to more uniformly distribute that load throughout the pumping cycle. It is a principal object of the present invention to eliminate or at least substantially reduce all of the aforesaid deficiencies found in the well pumping apparatus of the prior art.